Advanced ultrasonic NDE of composite airframe components: physics, modelling and technology

In recent years the use of composites in engineering has greatly increased due to the advantages which may be obtained. These are weight savings, increased strength, the ability to construct complex geometries and the use of mixed materials. Of particular interest in this work are carbon fibre reinforced plastics (CFRP) which are increasingly used in the aerospace industry. Historically, NDE methods for CFRPs have concentrated on through thickness measurements of ultrasonic attenuation or velocity to determine the presence of defects. Whilst this method is relatively fast and easy to employ there are significant disadvantages in terms of defect characterisation and the location of defects in three dimensions. The advent of full waveform capture and increased computing power allowing processing of large volumes of data, has made 3-D characterisation possible for the first time. The overall aim of this work is to develop new signal processing techniques with which to interpret ultrasonic signals from composite materials. The primary consideration is the propagation of normal incidence compression waves through the multi-layered composite structure, and the interaction of the waves with the various types of defect which may be present. The principal interest is the detection and classification of porosity. A multi-layered model of ultrasonic propagation in a composite is combined with a model which calculates the scattering response due to porosity. The model is used to simulate the ultrasonic signals that are obtained from NDE procedures applied to composite. The simulations are then used as the basis on which to develop novel signal processing schemes for the detection, location and characterisation of porosity and other types of defect. The response obtained from differing defect conditions is isolated and investigated using both time domain and frequency domain techniques. Comparisons are drawn between the responses obtained from modelling and from experimental samples. Consideration of the various methods which are sensitive to porosity leads to a system which can be applied to full waveform data to provide 3-D profiles of porosity and other defects. The work described in this thesis is covered by UK Patent Application Number 0818383.2

Advanced ultrasonic NDE of composite airframe components: physics, modelling and technology

In recent years the use of composites in engineering has greatly increased due to the advantages which may be obtained. These are weight savings, increased strength, the ability to construct complex geometries and the use of mixed materials. Of particular interest in this work are carbon fibre reinforced plastics (CFRP) which are increasingly used in the aerospace industry. Historically, NDE methods for CFRPs have concentrated on through thickness measurements of ultrasonic attenuation or velocity to determine the presence of defects. Whilst this method is relatively fast and easy to employ there are significant disadvantages in terms of defect characterisation and the location of defects in three dimensions. The advent of full waveform capture and increased computing power allowing processing of large volumes of data, has made 3-D characterisation possible for the first time. The overall aim of this work is to develop new signal processing techniques with which to interpret ultrasonic signals from composite materials. The primary consideration is the propagation of normal incidence compression waves through the multi-layered composite structure, and the interaction of the waves with the various types of defect which may be present. The principal interest is the detection and classification of porosity. A multi-layered model of ultrasonic propagation in a composite is combined with a model which calculates the scattering response due to porosity. The model is used to simulate the ultrasonic signals that are obtained from NDE procedures applied to composite. The simulations are then used as the basis on which to develop novel signal processing schemes for the detection, location and characterisation of porosity and other types of defect. The response obtained from differing defect conditions is isolated and investigated using both time domain and frequency domain techniques. Comparisons are drawn between the responses obtained from modelling and from experimental samples. Consideration of the various methods which are sensitive to porosity leads to a system which can be applied to full waveform data to provide 3-D profiles of porosity and other defects. The work described in this thesis is covered by UK Patent Application Number 0818383.2